This invention relates generally to semiconductor transistors, and more particularly the invention relates to laterally diffused MOS (LDMOS) transistors.
The LDMOS transistor is used in RF/microwave power amplifiers. The device is typically fabricated in an epitaxial silicon layer (P−) on a more highly doped silicon substrate (P+). A grounded source configuration is achieved by a deep P+ sinker diffusion from the source region to the P+ substrate, which is grounded. (See, for example, U.S. Pat. No. 5,869,875.)
The source resistance of the LDMOS transistor is determined in part by the mobility of positive carriers, or holes, in the P+ substrate. The source resistance is also sensitive to the drain-source voltage (Vds) and its effects. Further, a gold backside contact to the P+ substrate can require expensive preform compounds during packaging to maintain low source resistance.
The present invention is directed to reducing or eliminating these characteristics with conventional LDMOS transistors.